In conventional semi-submersible platforms, a load-supporting, rectangular deck-box structure is positioned upon the top of the columns. Operation modules are then placed on top of the deck-box structure. The deck-box structure offers a structurally solid design and may be of a sealed type which adds reserve buoyancy to the platform in an eventual damaged emergency state. However, a problem with this conventional design is that the operational modules have to be placed relatively high on the platform which leads to a high center of gravity for the platform. This results in a reduction in stability for the platform and as a consequence—a lesser pay-load, unless the size of the platform is increased as a compensation.
The semi-submersible platform is used for various services such as production of hydrocarbons, drilling and/or to provide accommodation for personnel. To provide these services, the platform is equipped with various equipment and systems, which may either be located directly in the deck-box structure or upon the the deck-box structure.
In a conventional semi-submersible platform, the operational modules—due to their size and to existing installation methods—are placed upon the deck-box structure, either by lifting or by an operation where the modules are skidded over from a barge.
However, from a construction and contracting point of view it can in certain cases be advantageous to locate the equipment and systems in separate operational modules that can be fabricated/contracted separately from the platform.
However, a disadvantage with this conventional design is that the operational modules have to be placed relatively high on the platform which leads to a high center of gravity for the operational modules, and accordingly for the completed platform. This results in a reduction in stability for the platform and as a consequence—a lesser pay-load, or alternatively the size of the platform has to be increased to compensate for the high vertical center of gravity of the operational modules. Furthermore, the weight and the size of these operational modules are normally such that there is only a limited number of devices available that can lift them, a fact that limits the number of available construction sites worldwide.